Peening is a process for improving properties of a metal surface. Peening is typically a cold work process, by which a mechanical pressure (hammer or shots) or blasts of light beam are applied to the metal surface. The energy transferred to the metal surface by the peening process is referred to as peening intensity.
Before starting peening of a component, a peening system is calibrated. A dummy component or a representative fixture is equipped with peening calibration holders. Standardized peening calibration strips are inserted into the peening calibration holders. During peening, the dummy component and the standardized peening calibration strip absorb energy generated by the peening process. After the peening process is performed on the dummy component, the peening calibration strips are removed from the calibration holders and bending (arc height) of the standardized peening calibration strips after peening is measured. A particular gauge is required for measuring arc height of the standardized peening calibration strips, as defined in publication J442_2013 from SAE International, revised on Feb. 18, 2013, titled “Test Strip, Holder, and Gage for Shot Peening”. The measured arc heights are plotted on a graph depicting the measured arc height versus peening time. This calibration process is repeated with new standardized peening calibration strips for at least four iterations. A curve, known as the saturation curve, is then identified through the measurements collected and plotted on the graph.
Peening intensity is most often determined using a 10% rule that states that intensity is the first arc height on the curve where the arc height increases by 10% for a doubling of time, as defined in publication J443_2010 from SAE International, revised on Jun. 16, 2010, titled “Procedures for Using Standard Shot Peening Almen Strip”. Finding the peening intensity with standardized peening calibration strips requires significant time: at least four iterations of peening standardized peening calibration strips, and manual arc height measurements, generation of graphs and several mathematical calculations that often lead to errors. Furthermore, the traditional peening calibration practices are misleading as most new users believe that the time to peen a part is related to the time required to peen the standardized peening calibration strips, whereas the time depicted rather reflects a measure of the kinetic energy transferred to the component. The traditional method is also detrimental to the environment as each standardized peening calibration strip is only used once and must then be discarded. Millions of standardized peening calibration strips per year are thus sent to the landfill.
Over the years, a few patents have described alternative devices to measure the energy transferred through peening. DeClark et al. in U.S. Pat. No. 4,470,292 has proposed a large plate on a cantilever rod with an analog deflection transducer to measure the deflection of the rod under the load of the gravity accelerated shot created by gravity peening. This method is not practical as it cannot be mounted on the component being peened to measure intensity directly on different points thereof. Matsuura et al. (U.S. Pat. No. 5,113,680) and Yamammoto et al. (U.S. Pat. No. 6,640,596) have proposed a single or dual level transducer for measuring an elastic wave caused by a shot collision. The proposed devices are too large, do not adapt to current standardized peening calibration strip holders, cannot be installed on existing dummy components, are complex, and include many parts such as wires that quickly wear in harsh peening environments.
There is therefore a need for a new peening calibration unit and system that resolve the above problems.